In direct current powered electrodynamic control systems, such as control systems for motors, for example, variations in the voltage of the direct current power supply causes variations in the motor output. In applications of motors in controlling a parameter of a physical system, such as temperature, for example, a temperature feedback signal in the motor control loop is used to regulate operation of the motor. In such systems voltage variations in the direct current power supply for the motor interfere with and degrade the closed loop regulation function, and require separate and independent correction.
In applications involving linear motors, such as those in resonant linear compressors, various control techniques are found. U.S. Pat. Nos. 3,819,874; 3,937,600; 4,067,667 and 4,345,442 describe linear compressors having provisions for piston stroke control. Applications of such linear compressors include their use in heat pumps, as described in U.S. Pat. No. 4,345,442. These heat pumps are used in systems for space heating and cooling, as in system applications in the control of the temperature in dwellings. These patents which represent prior art presently known to the applicants, are referenced herein since they are related to linear motor drives in temperature control systems. None, however, are related to or provide disclosures suggesting motor control by means of pulse width modulation, compensated for supply voltage variations, a feature of this invention.